1. Field of the Invention
The present invention relates to a method for producing an endoscope flexible tube, in particular, a method for producing a flexible tube constituting the insertion portion of an endoscope.
2. Description of the Related Art
In general, an endoscope includes a proximal operating portion and an insertion portion connected in series to the proximal operating portion. The proximal operating portion is held by an operator and the insertion portion is inserted into the body of a subject.
The insertion portion is constituted with, sequentially from the proximal operating portion, a flexible tube portion, a bent portion and a distal end portion. The distal end portion is provided with an optical observation system including lenses and prisms. The flexible tube portion allows the passage therethrough of a forceps channel for guiding the passage of treatment tools, bent wires, a light guide, signal cables and the like.
The flexible tube as the main part constituting the insertion portion of an endoscope is constituted with a spiral tube formed by spirally winding a metal strip, a cylindrical mesh sleeve covering the spiral tube and an outer coat, made of urethane resin or the like, laminated on the surface of the cylindrical mesh sleeve. For the purpose of facilitating the insertion into the body, the distal end portion of the insertion portion is required to be high in flexibility and the flexible tube of the insertion portion is required to be low in flexibility and high in hardness in the side of the proximal operating portion. An endoscope is used repeatedly, and hence cleaned and sterilized. Therefore, the insertion portion is required to be heat resistant and chemical resistant.
Japanese Patent Application Laid-Open No. 2001-161632 discloses a case where the outer coat of the flexible tube includes as the main polymer thereof one or two of a thermoplastic polyurethane elastomer, a thermoplastic polyolefin elastomer and a thermoplastic polyester elastomer, for the purpose of enhancing the heat resistance and the chemical resistance of the insertion portion. However, when the main polymer includes only one material, there is a problem that the heat resistance, the chemical resistance and the operability are not satisfied simultaneously. On the other hand, when the outer coat is made of a mixture, there is a problem that the material low in heat resistance and chemical resistance may be located in the outside portion of the outer coat, and hence the insertion portion may be poor in heat resistance and chemical resistance.
Japanese Patent Application Laid-Open No. 2001-161633 discloses the constitution of the outer coat of the flexible tube with a mixed material composed of a thermoplastic polyurethane elastomer and a thermoplastic polyester elastomer, for the purpose of enhancing the heat resistance and the chemical resistance of the insertion portion. However, when the outer coat is formed of such a mixture, there is a problem that the material low in heat resistance and chemical resistance may be located in the outside portion of the outer coat, and hence the insertion portion may be poor in heat resistance and chemical resistance.
Japanese Patent Application Laid-Open No. 2001-333883 discloses a constitution of the outer coat with a laminate composed of an outer layer, an inner layer and an intermediate layer, and a partition of the intermediate layer into a plurality of regions through the intermediary of boundaries, for the purpose of enhancing the operability, the chemical resistance and the durability of the insertion portion. However, there is a problem that the lengthwise partition of the intermediate layer into the plurality of regions degrades the insertion performance.
Japanese Patent Application Laid-Open No. 2002-058637 discloses a lengthwise partition of the flexible tube into a plurality of regions and a weight reduction of the distal end portion as compared to the proximal portion. However, there is a problem that the lengthwise partition into the plurality of regions degrades the insertion performance.
Japanese Patent Application Laid-Open No. 2006-000281 discloses a control of the infiltration of an adhesive to the blade by specifying the annealing conditions or the aging conditions. However, there is a problem that the variation of the flexibility with time is large.
Japanese Utility Model Application Laid-Open No. 55-112505 discloses a flexible tube, provided with an outer coat, having a two layer structure composed of a soft resin layer and a hard resin layer wherein the proportion of the soft resin layer is increased in the side of the distal end of the flexible tube and the proportion of the hard resin layer is increased in the side of the proximal operating portion of the flexible tube. However, there is no specific disclosure of the fact that under what conditions a mesh-shaped tube is coated with the soft resin layer and the hard resin layer.